Plastic bottles and other articles made by blow molding are formed from a tubular section of parison which is extruded from a die and then clamped between a pair of mold sections. The bottom of the parison is squeezed together by the two mold sections and, as a result, is sealed together to form a closed bottom of the bottle. The top of the parison becomes the neck of the bottle and is typically kept open to allow for insertion of a blow pin. After the bottle has been formed and cured, the mold sections are separated and the bottle either drops under the force of gravity into a receptacle or is removed by a take-off mechanism. U.S. Pat. No. 4,998,873, issued Mar. 12, 1991 to M. W. Martin et al. describes the construction and operation of an indexable blow molding machine suitable for carrying out this process.
Once the bottle has been removed from the mold, excess material located at the mouth of the bottle must be cut away and removed for disposal or recycling. Since many of the articles produced by blow molding are used in the food industry to store beverages and other foodstuffs, it is particularly important that the excess material be cut away and removed without it or fragments of it falling into the bottle.
The excess material at the mouth of the bottle can be formed during the blow molding process into a predetermined shape that remains attached to the neck of the bottle. Sometimes the excess material is formed into a conical (dome) or other rotationally symmetrical shape so that so that an oscillating cutter head can be used to trim the excess material from the bottle. In a known prior art cutting machine, the cutter head includes a cutter that is brought into contact with the neck of the bottle while the cutter head rotates through 360.degree. to trim the excess material, which then falls away under the force of gravity. Rotation is controlled by a rotary actuator with the direction of rotation being reversed for each successive bottle due to the reciprocation of the rotary actuator.